Field of the Invention
The present invention relates to a method for coloring of anodic aluminum oxide (AAO) surface, especially to a method for dye-free coloring of one-time anodic aluminum oxide surface.
Descriptions of Related Art
Anodic aluminum oxide (AAO) is an aluminum oxide material with hexagonal pore arrays and is broadly applied to nanowire synthesis, nanofabrication, quantum dot fabrication etc. Generally, aluminum anodizing is an electrochemical process in which a compact aluminum oxide layer (AAO film) is built on the surface of aluminum or aluminum alloy. Thus an AAO substrate is formed. The compact AAO film not only protects the inner aluminum or aluminum alloy from further oxidation but also increases resistance to corrosion and wear, surface hardness and appearance properties of the aluminum-based material. The AAO substrate is widely used in housings of electronic or 3C products owing to the advantages mentioned above. In order to increase the aesthetic appearance of the housing of electronic or 3C products, structural colors of AAO have received considerable attention in recent years.
The AAO with structural colors available now are produced by at least two-time anodization of a thick/or high-purify aluminum (or aluminum alloy) substrate. Thus a regular array of nanopores is obtained and dyes or other materials can be filled into the nanopores to get specific colors of the substrate. Moreover, the anodizing is an exothermic reaction. Thus anodization is carried out in acidic solution at low temperature (−1 to 10° C.) to prevent damages of the nanoporous structural caused by Joule heat generated during the process. For example, China Patent No. 102181902 “Method for coloring aluminum and alloy surface thereof” issued on 16 Jan. 2013, disclosed a method of coloring the aluminum alloy surface by two-time anodization at a temperature of 0° C. to 5° C.; however, it must conduct the 2nd-time anodization with 50-300 periods of continuous 5-step anodization for coloring aluminum and alloy surface; Taiwan Patent No. I248479 “Aluminum product with film capable of varying color according to change of visual angle and method for forming film capable of varying color according to change of visual angle on aluminum basis metal base material” issued on 1 Feb. 2006, disclosed a method of carrying out anodic oxidation treatment on the aluminum basis metal base material to provide an anodic oxidation film of aluminum comprising a porous layer and a barrier layer and depositing the metal deposition in the holes of the porous layer for performing electrolysis coloration of anodic oxidation film of aluminum; however it conducts two- or three-time anodization with sulfuric acid and phosphoric acid. Therefore the production process of the colored substrate takes time and cost. Additionally, some other patents such as Taiwan patent publication No. 201227822 “Method for manufacturing nano-structure patterned substrate” issued on 1 Jul. 2012, disclosed the following steps of growing an aluminum film directly on a substrate, then using two-time anodic oxidation method to process the aluminum film to an anodic oxidized aluminum layer with nanometer hole structures; Taiwan patent publication No. 200722559 “Metal nanodot arrays and fabrication methods thereof” issued on 16 Jun. 2007, disclosed a method to deposit a block copolymer of polymer film on a conductive substrate, then deposit the metal material in the nano pore by electroplating process and U.S. patent publication No. 20090242410 “Method for electrochemical plating and marking of metals” provided a electrochemical plating process to electroplating the metal surface with the electroplating solution. These prior arts has disclosed the electroplating process, but none of these prior arts mentioned technique for coloring on the substrates.